Generally, an engine temperature is used as an important parameter used for a known temperature control system for an internal combustion engine. However, in practice, a cooling water temperature (i.e. a coolant temperature) is used as a value representing the engine temperature. In the known temperature control system for the internal combustion engine, various controls of the internal combustion engine are executed on the basis of the cooling water temperature, which is detected by a water temperature sensor. Therefore, detecting a malfunction of the water temperature sensor (i.e. a fluid temperature detecting means) is crucial. Accordingly, various methods and devices for detecting the malfunction of the water temperature sensor have been suggested.
For example, a fault diagnostic device for a water temperature sensor disclosed in JPH10-073047A is configured to determine that a malfunction such as a characteristic displacement and the like occurs at the water temperature sensor in a case where a cooling water temperature, which is detected by the water temperature sensor when a predetermined time has been elapsed since an internal combustion engine is started, is lower than a reference value.
According to an abnormality detection device of a temperature sensor disclosed in JP2007-192045A, a soaking time of an internal combustion engine necessary for a difference between a temperature detected by a water temperature sensor and a temperature detected by an intake air temperature sensor to fall within a range of a predetermined temperature difference after the internal combustion engine is stopped is set to a predetermined time. The abnormality detection device determines that the water temperature sensor and the intake air temperature sensor are both in a normal state in a case where the temperature difference between the temperature detected by the temperature sensor, which detects a cooling water temperature of the internal combustion engine, and the temperature detected by the intake air temperature sensor, which detects an intake air temperature of the internal combustion engine, falls within the predetermined range in a case where a down time of the internal combustion engine reaches a predetermined time. On the other hand, in a case where the temperature difference falls outside the range of the predetermined temperature difference, the abnormality detection device determines that a malfunction occurs at either one of the water temperature sensor and the intake air temperature sensor. Furthermore, even in a case where a block heater is attached at an engine block in order to partially heat a cooling water in the vicinity of a combustion chamber while the internal combustion engine is stopped, the temperature sensor detects a temporal decrease of the temperature, which is detected by the water temperature sensor, during a predetermined temperature fluctuation period immediately after the internal combustion engine is started in order to avoid a mis-determination of a state of the water temperature sensor and the intake air temperature sensor.
Disclosed in JP2008-298058A is a control device of an internal combustion engine having a block heater determining means, which is configured so as to determine whether or not a block heater is electrified (used) while the internal combustion engine is being stopped on the basis of changes in a cooling water temperature immediately after the internal combustion engine is started or on the basis of changes in a rotational speed of the internal combustion engine.
According to the above-described known temperature control systems, the malfunction of the fluid temperature detecting sensor, which detects the fluid temperature of the coolant, is detected on the basis of the changes in the temperature, which is detected by the fluid temperature sensor and which may occur due to a circulation of the coolant that is heated within the internal combustion engine and whose post-heating is extracted. Therefore, a process for determining the malfunction of the fluid temperature detecting sensor and the process for determining a usage of the block heater are executed under the assumption that the coolant is circulated.
There exists a technology to effectively perform a warm-up drive in a manner where the warm-up drive is performed while a circulation of a cooling water is stopped. For example, the warm-up drive may be achieved in a manner where an electric pump is adapted as a pump for circulating the cooling water and the electric pump stops the circulation of the cooling water independently of a drive of an internal combustion engine. Furthermore, a thermostat (or a combination of an fluid temperature sensor and a control valve, which are configured independently of and separately from each other) may be provided on a coolant circulating passage, which is used for circulating the cooling water between the internal combustion engine and a radiator. For example, the thermostat is closed to stop the circulation of the cooling water between the internal combustion engine and the radiator while a coolant temperature is lower than a predetermined temperature in order to achieve the warm-up drive for promptly increasing the coolant temperature at the internal combustion engine. Accordingly, in the case where the circulation of the cooling water is stopped when the internal combustion engine is started, the above-described process for detecting the malfunction of the fluid temperature sensor and the process for determining the usage of the block heater may not be executable.
A need thus exists for a temperature control system for an internal combustion engine which is not susceptible to the drawback mentioned above.